Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
FIG. 1 illustrates a packaged phosphor-converted light emitting device described in more detail in U.S. Pat. No. 8,680,556. FIG. 2 illustrates the composite reflective layer of FIG. 1 in more detail. The device of FIG. 1 includes an LED 302 disposed on package 300 and covered by an encapsulant 304 that includes phosphor. Light emitted out of the LEDs 302, light emitted from phosphors in the encapsulant 304, and light which reflects off of the exit surface of the encapsulant 304 may be emitted towards the substrate 300. At least a portion of this light is reflected off a composite layer 362 and redirected so that it can exit the package.
FIG. 2 shows one possible configuration of a reflective composite layer 362. In this configuration, a set of dielectric layers 308 is formed over a set of metal layers. The portion of the dielectric layers 308 adjacent to the metal layer 310 may be an adhesion layer 312. The portion of metal layer 310 adjacent to the substrate 300 may also be an adhesion layer 312. In the embodiments described in U.S. Pat. No. 8,680,556, the material in the composite layer closest to substrate 300 is silver.